Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure – With particular semiconductor material
Reexamination Certificate
2003-12-22
2004-10-26
Crane, Sara (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
With particular semiconductor material
C257S089000, C257S090000
Reexamination Certificate
active
06809347
ABSTRACT:
TECHNICAL REALM
The invention relates to a light source with a light-emitting element that emits in a first spectral realm, preferably in the blue and/or ultraviolet range of that visual spectrum, and with a luminophore that either is derived from the group of alkaline-earth ortho-silicates or that contains at least a component from this group of luminescent materials that absorbs a portion of the emission from the light-emitting element and then emits in another region of the spectrum, preferably in the yellow-green, yellow, or orange ranges. The luminophore selected may also be used in mixtures with other luminophores from this group and/or with other luminescent materials that do not belong to this group.
The light-emitting element is preferably an inorganic light-emitting diode (LED), but may also be an organic LED, a laser diode, and inorganic thick-layer electro-luminescence film, or an inorganic thin-layer electro-luminescence component.
STATE OF THE ART
Inorganic LED's distinguish themselves by, among other things, long service life, low space requirements, insensitivity to vibration, and narrow-band spectral emissions.
Numerous emission colors, especially wide-band spectral colors, cannot be realized from LED's because of the intrinsic emission of an active semiconductor material, or can only be inefficiently realized. This especially applies to the creation of white light.
In accordance with the state of the art, emission colors that cannot be intrinsically realized by a semiconductor are created using color conversion.
The technique of color conversion is essentially based on the principle that at least one luminophore is positioned above the LED “die.” It absorbs a portion of the emission from the die, and is thus excited to photo-luminescence. The emission or light color of the source then results from the mixing of the emission transmitted from the die with the emission emitted from the luminescent material.
Either organic or inorganic systems may basically be used. The significant advantage of inorganic pigments is their higher chemical, thermal, and emission stability in comparison to organic systems. In connection with the long service life of inorganic LED's, long-life inorganic luminophores ensure a high level of color stability of the light source consisting of both light sources.
If the emitted emission from LED's emitting blue is to be converted into white light, luminescent materials are used that effectively absorb the blue light (450-490 nm) and convert it into predominantly yellow luminescent emission. However, there is only a limited number of inorganic luminophores that meet these specifications. At this time, materials from the YAG class of luminescent materials are used as color conversion pigments for blue LED's (WO 98/05078; WO 98/05078; WO 98/12757). These, however, include the disadvantage that they possess a high degree of efficiency only at an emission maximum of less than 560 nm. For this reason, only cold white light colors with color temperatures between 6,000 K and 8,000 K, and accordingly with comparatively reduced color reproduction (typical values for color reproduction index Ra lie between 70 and 75), may be used with the YAG pigments in combination with blue diodes (450-490 nm). This results in severely-limited application possibilities. On the one hand, higher demands are imposed as a rule during application of white-light sources for general illumination, and on the other, consumers in Europe and North America prefer warmer light colors with color temperatures between 2,700 and 5,000 K.
It is further known from WO 00/33389 to use Ba
2
SiO
4
:Eu
2+
among others as a luminophore to convert the light from blue LED's. The maximum of the emission from the Ba
2 SiO
4
:Eu
2+
luminescent material is, however, 505 nm, so that white light cannot be reliably created using such a combination.
In works by S. H. M. Poort et al.: “Optical Properties of Eu
2+
-activated orthosilicates and orthophosphates,” Journal of Alloys and Compounds 260 (1997), pp. 93-97, the characteristics of Eu-activated Ba
2
SiO
4
and of phosphates such as KBaPO
4
and KSrPO
4
are investigated. It was also determined here that the emission from Ba
2
SiO
4
is about 505 nm.
PUBLICATION OF THE INVENTION
The task of this invention is to alter a light source of the type mentioned at the outset so that white light colors with warmer color temperatures, especially those color locations that lie within the tolerance ellipses established by the CIE for general illumination may be created under conditions of high luminous efficiency and a high degree of color reproduction quality.
This task is solved by a light source based on the invention of the type mentioned at the outset so that the luminophore is an alkaline-earth ortho-silicate activated with bivalent Europium of the following composition:
(2-x-y)SrO·x(Ba
u
, Ca
v
)O·(1-a-b-c-d)SiO
2
·aP
2
O
5
bAl
2
O
3
cB
2
O
3
dGeO
2
:yEu
2+
where
0≦x<1.6 0.005<y<0.5x+y≦1.6
0≦a,b,c,d<0.5 u+v=1
applies;
and/or an alkaline-earth ortho-silicate of the following composition:
(2-x-y)BaO·x(Sr
u
, Ca
v
)O·(1-a-b-c-d)SiO
2
·aP
2
O
5
bAl
2
O
3
cB
2
O
3
dGeO
2
:yEu
2+
where
0.01<x<1.6 0.005<y<0.5
0≦a,b,c,d<0.5 u+v=1 x·u≧0.4
applies, whereby preferably at least one of the values a, b, c, and d is greater than 0.01. A portion of the Silicon may be replaced by Gallium in both formulas.
Surprisingly it has been found that white light with good color reproduction and a high degree of luminous efficiency may be realized through a combination of a blue LED with a luminophore selected from a group of alkaline-earth ortho-silicates activated with Europium of the above-named composition based on the invention. In contrast to luminophores based on pure Barium ortho-silicates that emit bluish-green light, yellow-green and yellow to orange luminescent light may be created using Barium-Strontium-orthosilicate mixed crystals, and even completely orange luminescent light may be created by incorporation of Calcium into the ortho-silicate crystal lattice, so that, by mixing the transmitted light from the blue LED with the luminescent light from the selected luminophore, white light with good color reproduction and a high degree of luminous efficiency may be generated. Displacement of emission color by means of substitution of Ba with Sr in ortho-cilicates has previously been known only for excitation using hard UV emission (254-nm excitation) from the above-mentioned work by Poort et al. No description was made of the fact that this effect surprisingly occurs more strongly under irradiation with blue light in the range of 440-475 nm. Ba—Sr—Ca ortho-silicate mixed crystals and their strong emission capability under excitation with low-frequency UV emission or blue light were previously completely unknown.
The selected luminophore may also be used in mixtures with other luminophores of this group and/or with additional luminescent materials not belonging to this group. The latter luminophores include, for example, blue-emitting alkaline-earth aluminates activated using bivalent Europium and/or Manganese, along with the red-emitting luminophores of the group Y(V,P,Si)O
4
:Eu,B
1
, Y
2
O
2
S:Eu,Bi, or :Eu
2+
,Mn
2+
alkaline-earth Magnesium di-silicates activated with Europium or Manganese according to the formula
Me
(3-x-y)
MgSi
2
O
8
:xEu, yMn,
whereby
0.005<x<0.5 0.005<y<0.5
and Me═Ba and/or Sr and/or Ca applies.
As will be shown in the following embodiment examples, the Sr component in the mixed-crystal luminophores based on the invention must not be too small in order to be able to generate white light.
Surprisingly, it has further been found that the additional inclusion of P
2
O
5
, Al
2
O
3
, and/or B
2
O
3
into the crystal lattice, as well as the substitution of a portion of the Silicon by Germanium, may also have a significant influence on the emission spectrum of a given luminophore, so that this may b
Kempfert Wolfgang
Pachler Peter
Roth Gundula
Starick Detlef
Tasch Stefan
Crane Sara
Leuchtstoffwerk Breitungen GmbH
Wieczorek Mark D.
LandOfFree
Light source comprising a light-emitting element does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Light source comprising a light-emitting element, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Light source comprising a light-emitting element will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3332835